The purpose of this project was to study the effect of aging, stress and antihypertensive drugs on the neuronal activities of both the central and peripheral catecholaminergic nervous systems and on the function of the cardiovascular system. (1) An age-dependent increase in blood pressure was found in spontaneously hypertensive, in Fisher-344 and in Wistar rats. (2) Immobilization stress induced increases in plasma catecholamines, corticosteroid and blood sugar that were not correlated significantly with age of animals. The aged group appeared to have a slowed rate of release of these substances into the circulation. (3) Stress produced an Alpha-adrenergic vasopressor response in young rats but a Beta-adrenergic vasodepressor response in old rats. Over 90% of the old rats died within 12 hours after 30 minutes of immobilization stress. The stress-induced increase in heart rate was significantly reduced with age. (4) The age-dependent increase in blood pressure was effectively decreased by the administration of Uncarine A, the active ingredient of a Chinese herbal medicine. It reduced the blood pressure of hypertensive but not normotensive animals for up to 48 hours.